Document processing systems refer to a set of devices that construct, produce, print, translate, store, and archive documents and their constituent elements. Such devices include printers, scanners, fax machines, electronic libraries, and the like. The present invention addresses situations particularly relevant to printing systems and discusses them as the prime example of a document processing system, but the present invention should not be construed to be limited to any such particular printing application. Any document processing system is intended to benefit from the advantages of this invention.
A digital print system renders a digital image, consisting of electronic data, to a human readable document comprised of one or more printed pages. Digital print systems typically include: 1) a print controller and 2) an image output terminal (“IOT”). The print controller may receive electronic data for a print job from various sources, including an individual computer, a distributed computer network, an electronic storage device, a scanner, or any other device capable of communicating the data to the print controller. The print controller may also generate electronic data for a print job. Regardless of the source of the electronic data, the print controller translates it to digital image data compatible with the IOT and transmits the digital image data to the IOT. The print controller also controls operations within the IOT. The IOT is typically further comprised of one or more feeding stations, a print engine with a plurality of imaging stations, and one or more finishing stations. Such feeding stations, imaging stations, and finishing stations can generally be referred to as processing stations.
Digital print systems are well known to the fields of incremental printing of symbolic information, photocopying, facsimile, and electrophotography. Digital print systems are also referred to by many technical and commercial names within these fields, including: electrophotographic printers, copiers, and multifunction peripherals; xerographic printers, copiers, and multifunction peripherals; digital presses; laser printers; ink-jet printers; and thermal printers. Examples of some recent patents relating to digital print systems include Xerox Corporation U.S. Pat. Nos. 5,629,775, 5,471,313, and 5,950,040.
U.S. Pat. No. 5,629,775, incorporated herein by reference, discloses an electronic image processing apparatus having a marking machine, a source of copy sheets, a controller, and a plurality of resources wherein each of the resources includes an associated processor for storing data related to the operational timing of the associated resource. A bus interconnects the processors to the controller for directing the operation of the image processing apparatus to provide images on the copy sheets and the controller includes circuitry for interrogating each of the processors for the operational timing data and logic for responding to the operational timing data of each of the processors for dynamically configuring the controller to operate in accordance with the operational timing of the processors.
U.S. Pat. No. 5,471,313, incorporated herein by reference, uses a control system for an IOT with a hierarchical structure that isolates subsystem controls for purposes of efficient algorithm design, analysis and implementation. The architecture is divided into three levels and has a controls supervisor that provides subsystem isolation functions and reliability assurance functions. The architecture improves image quality of IOT outputs by controlling the operation of the IOT to insure that a tone reproduction curve of an output image matches a tone reproduction curve of an input image, despite several uncontrollable variables which change the tone reproduction curve of the output image.
U.S. Pat. No. 5,950,040, incorporated herein by reference, discloses a feedback control system that controls developability of a xerographic imaging device using optical sensors for measuring development values based on an expected target value. The feedback control system includes a controller device and a feed-forward device. The controller device includes an input summing node, a gain device, an integrator and a nominal summing node which are serially connected in communication with each other. The input summing node, the gain device and the integrator are operative in combination with each other to receive and process the measured value and the target value to provide a new corrected actuator value to the integrator summing node. The feed-forward device is connected to the nominal summing node and receives and responds to the target value to output a nominal actuator value to the nominal summing node. The nominal summing node combines the new corrected actuator value and the nominal actuator value to provide an actuator value to the xerographic imaging device for controlling the developability of the xerographic imaging device. A method for controlling developability of a xerographic imaging device is also described.
The ultimate goals of any digital print system are to deliver outstanding print quality in both black and color output, to reliably printjobs exploiting the capabilities of the print system, to minimize waste and downtime, and to accomplish these goals by consistently and automatically performing repetitive document processing functions. A comprehensive approach to addressing these goals would be to adopt a system architecture and a method for verifying the correctness of various document processing processes in the digital print system. Such an approach could address correctness, quality, and efficiency in each phase of document processing in a common manner. For example, problems related to: 1) verifying the integrity of documents prior to distribution, 2) establishing correct operational set points for the digital print system, and 3) supporting the retrieval and reconstruction of documents after distribution—could be simultaneously solved by this comprehensive approach. The following paragraphs identify current problems in each of these three areas and corollary needs for improvements.
First, problems regarding verifying the integrity of documents prior to distribution are addressed. The popularity of personalizing short documents produced by a digital print system, often in high volume for numerous people, by merging data from a computerized database with a digital form has increased the importance of verifying document integrity and the need to warrant that a digital print system correctly processes documents. This entails not only ensuring that the actual sequence of printed pages corresponds to the intended page sequence for the job, but also includes verification that the image printed on each page matches the desired image content for the page. More specifically, document integrity includes verifying: 1) the document does not contain duplicate pages, 2) the document is not missing pages, 3) the pages of the document are in the proper order, 4) the printed image matches the desired image content, 5) undesired duplicate documents were not produced, 6) no desired documents are missing, and 7) documents are in the proper order.
Some digital print systems currently depend on manual verification of document integrity. Examples of manual verification include: a) personalized print jobs where each page contains a person's name and/or identification number and operators manually verify that the document pages are for the correct person, that they are in the proper sequence, and that the correct document is matched with a personalized envelope and b) printing books on demand, including printing a single book, where the entire book is manually inspected after it is completely bound. In either example, the manual inspection operation is labor intensive and performed at a time when identification of a defect results in a complete rerun and significant loss of time and profit.
Current attempts to automate verification of document integrity are well short of the efficiency and flexibility needed for digital print systems. To date, such attempts are based on standardized reference parameters, are relatively inflexible, and are not sensitive to the unique content of a given document. This severely limits the ability of the digital print system to adapt to the diverse range of documents being produced and presented for processing in today's information intensive environment. Typically, automated recognition and verification equipment in such digital print systems operate with little or no knowledge of the content of the document or the expected imaging result from processing the document. In the personalized print job example, suppose the inspection process is automated. Further, suppose the recognition equipment recognizes that the person's name and identification number on the document is “Name/1234”. With only this information, there is no way of determining the complete “truth,” i.e., whether this page has the correct predecessor and successor pages and whether it is matched with the correct envelope. Of course, the automated inspection process might be enriched to include these additional verification steps. For example, by looking for “Name/1234, Page 2 of 4” and using a built-in counter to assure that consecutive sheets are delivered with the same name and identification the digital print system could verify the integrity of the sequence of each page of the document. However, this achieves only a partial solution and is ad hoc, tremendously inflexible, and not closed loop with respect to the print job.
Consequently, a need exists for a digital print system architecture that enables verification of document integrity during the printjob with an improved degree of flexibility from document to document. Furthermore, a need also exists to extend such document integrity verification capabilities to any printjob which may be performed on the digital print system with an improved degree of flexibility from print job to print job.
Next, problems regarding setting up the digital print system are addressed. In order to maintain each station of the digital print system at certain quality standards, setup procedures are usually performed after installation, after a certain period of operation, and after certain maintenance procedures, particularly for imaging stations within the print engine. Color print engines, for example, require setup procedures to maintain color image quality and consistent repeatability from job to job. The setup procedures commonly employed by color print engines include: 1) a calibration process, 2) closed-loop imaging station control, and 3) print engine profiling.
First, under the calibration process, color print engines typically adjust and align imaging stations of each of the multiple color separations. In general, the calibration process for color print engines typically involves one or more print/adjust cycles, each cycle usually consisting of four steps: 1) printing one or more test targets, 2) measuring the test target with a sensor, 3) adjusting print controller imaging or one or more imaging stations of the print engine based on differences between measured and expected values, and 4) updating print controller tables.
Second, closed-loop imaging station control involves printing one or more standard or pre-programmed color test targets, measurement of certain parameters of the printed test targets, and image station tuning based on differences between measured values and the expected values for the test targets. Frequently, such test targets and closed-loop controls work on the cyan (C), magenta (M), yellow (Y), and black (K) imaging channels independently.
Finally, color printers carry the special requirement of publicizing their color capabilities in a standard format known as an International Color Consortium (ICC) profile. Such profiles define the imaging results of various mixes of multiple color separations in the print controller/print engine combination. This is accomplished through print engine profiling, where the profile is made by measuring printed color test targets, computing color correction factors, and storing such factors in ICC profile format. Profiling differs from calibration because it simply describes the current print engine state without attempting to adjust or tune imaging stations to comply with nominal “factory” imaging standards.
In all three cases, the trend is to automate setup procedures in order to reduce the operator skills required for processing production color documents. Density and color measuring devices and comparators to compare measured values to pre-established reference values or values stored in lookup tables are commonly included in advanced print engine designs to facilitate automation. However, a digital print system architecture that enables the source of the test target image to serve the dual function of acting as the reference for expected values being compared to measured values of the image actually printed would simplify print engine setup procedures and the overall system design supporting such procedures. Consequently, a need exists for a digital print system architecture that enables simplified print engine setup procedures to be employed and reduces the complexity of the overall system design supporting such procedures.
Finally, problems regarding verifying integrity of documents after distribution are addressed. Digital print systems that produce printed documents by employing variable print and last second merging of data with digital forms frequently are required to keep a digital copy of the resulting document set. This is required to accommodate subsequent reference to the processed document, such as the “customer service” problem in which a customer calls to question some aspect of an account statement or other personalized document that was printed by merging personalized data with a standardized form. Without a copy of the customer's personalized document, a customer service representative can only access the customer's database record as of the time of the inquiry. This can lead to confusion if there is no audit trail in paper files or electronic media indicating that the customer's personalized document was actually generated and mailed. Image filing mechanisms have been instituted to solve this problem. However, current image filing mechanisms typically involve multiple digital print system add-on components and are often prone to operator errors due to the complex interactions required to regenerate the customer's personalized document. Consequently, a need exists for a digital print system architecture that enables simplified electronic archive and retrieval operations to validate and possibly regenerate previously distributed documents.